A nitride semiconductor electronic device has a high breakdown voltage and a small ON resistance compared to a conventional semiconductor electronic device, and its application to a compact and low-loss switching power source has been expected. Especially, a nitride semiconductor device that includes a hetero-interface between an undoped GaN layer and an undoped AlGaN layer exhibits a low-loss characteristic, owing to the two-dimensional electrons accumulated at the hetero-interface with high mobility and high concentration.
A switching element and a rectifying element are required in the switching power source circuit. When using an AlGaN/GaN field effect transistor so called high electron mobility transistor (HEMT) as the switching element, it is preferable to combine an AlGaN/GaN Schottky diode therewith, since both have breakdown voltages at about the same degree and operate at high speed.
However, the AlGaN/GaN Schottky diode has a large leak current under a reverse bias compared to a typical silicon Schottky diode. The reverse leak current of the AlGaN/GaN Schottky diode is low by about three figures compared to a forward current, whereas a reverse leak current of the silicon Schottky diode is low by about five figures. Hence, a reduction of the leak current is strongly desired in the AlGaN/GaN Schottky diode.